What was the original name for Halloween?

The Halloween tradition began with the ancient Celtic festival of Samhain, meaning "summer's end, which was a feast to celebrate the harvest. At that time people would put on costumes to ward off evil spirits and ghosts. In May of 609 Pope Boniface IV converted the Pantheon in Rome into a Christian church. The church was consecrated by the pope to the Virgin Mary and all the Martyrs. The Pantheon was a temple erected as a tribute to Jupiter the Avenger, Venus, and Mars. The day became known as "All Martyr's Day"

In the eighth century Pope Gregory III designated November 1 as a time to honor all saints as well as martyrs. The day became known as All Saints (hallows) Day and the night before as All Hallows Eve and eventually Halloween.

In those early days, it was thought the souls of the dead would revisit their homes seeking hospitality. Places would be set at the table for them. However it was also thought evil spirits would wander looking for bodies to possess for the next year. Dressing as witches, ghosts, goblins they could avoid being possessed.

In Colonial New England, the first celebrations were also held to celebrate the harvest, where neighbors would eat, share stories of the dead, dance and sing.

In the 1800's borrowing from Irish and English customs, Americans began to dress in costumes and go door to door asking for money or food, thus began "Trick or Treat"